Products > Test Equipment
Picotest Injector Teardowns
sixtimesseven:
--- Quote from: Jay_Diddy_B on May 21, 2020, 11:31:20 pm ---Hi group,
been busy with KiCAD and Fusion 360.
Any interest in this project:
(Attachment Link)
(Attachment Link)
This is a blocking capacitor and bias injector.
Regards,
Jay_Diddy_B
--- End quote ---
Yes, very interesting indeed! Just found this thread. Great work! I made my own PSSR tester since the picotest unit was far to expensive for me. Ended up doing pretty much what Ti suggested:
http://www.ti.com/lit/an/slaa414a/slaa414a.pdf?ts=1590175942099
Jay_Diddy_B:
Hi,
Let me share a few measurements made on the prototype:
This is a picture of the prototype. It was milled on double sided FR4 PCB. The board is 100mm x 100mm
0 - 200MHz
A DSA815-TG was used for the measurement. The setup was normalized with a BNC barrel connector.
The Bias tee is almost perfectly flat in the frequency range 0 - 200MHz.
This was confirmed using an HP3577A VNA
0 - 1.5GHz
The frequency range was widened to 1.5 GHz
There is a notch at 922MHz
After a little while I realized what was causing this.
I tested a BNC tee piece with an 8cm length of RG316 coax on one limb.
This is the result:
A notch at 625MHz
This notch is when the open length of the line is 1/4 of wavelength.
3 x 10E8 /625 x 10E6 = 48cm
1/4 wavelength = 12cm
velocity factor = 0.66
It kind of works out.
At 922MHz
wavelength = 3 x 10E8 / 922 x10E6 = 32cm
quarter wavelength = 8cm
Open circuit transmission line
The resistor needs to be moved closer to the capacitors.
Regards,
Jay_Diddy_B
Jay_Diddy_B:
Hi,
The bias line was cut in this location:
And the measurement repeated:
Same vertical scale 5dB/div
Considerable improvement.
Some of the other 'wiggles' will go away if I have more vias between the top and bottom planes.
Regards,
Jay_Diddy_B
Sighound36:
Hi Jay
As with all things RF, some of the smallest movements generator some of the most obvious gains.
Great work :-+
Jay_Diddy_B:
Hi,
I have continued to look at this.
I have been thinking about the best way to connect the large number of capacitor in series / parallel and maintain a controlled impedance.
PCB Design
Prototype board
The board was made from 0.062 FR4 on my LPKF Protomat c60.
Board Assembly
I inserted some of the 'via wires'
Measurement
I used an HP 8714 for the measurement:
This is 3mHz to 3GHz 2dB/div.
looking good!!
Jay_Diddy_B
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